Vic Lib leader sorry for anti-gay letter

Victorian Opposition Leader Matthew Guy says he apologised at the time for signing an "inappropriate" homophobic letter as a student activist, but the government says it reveals "deep seated attitudes".

More than two decades after the now-Liberal leader put his name to the letter, the issue has resurfaced eight months out from a state election.

"We view your organisation with distaste and see it as a sign of a very sick society suffering from severe moral decay," read the letter from the La Trobe University Students' Representatives Council, co-signed by Mr Guy, to the Gay and Lesbian Immigration Task Force.

"It is a shame that organisations such as yours exist."

Mr Guy told reporters on Thursday the letter was written in 1994 and he apologised soon after "because I realised it was inappropriate".

"That's why I apologised in 1994 when I was 20," he said.

Labor's Deputy Premier James Merlino said it was a "disgraceful" letter.